Protection of switched capacitor power converter

ABSTRACT

Transient or fault conditions for a switched capacitor power converter are detected by measuring one or more of internal voltages and/or currents associated with switching elements (e.g., transistors) or phase nodes, or voltages or currents at terminals of the converter, and based on these measurements detect that a condition has occurred when the measurements deviate from a predetermined range. Upon detection of the condition fault control circuitry alters operation of the converter, for example, by using a high voltage switch to electrically disconnect at least some of the switching elements from one or more terminals of the converter, or by altering timing characteristics of the phase signals.

CROSS REFERENCE TO RELATED APPLICATION

This application claims priority to U.S. application Ser. No. 13/838,681filed Mar. 15, 2013, the contents of which are hereby incorporated byreference in their entirety.

BACKGROUND

This invention relates to protection of switched capacitor powerconverters.

Various configurations of switched capacitor power conversion circuitsprovide voltage conversion (i.e., step up, step down, or bidirectional)between a high side voltage and a low side voltage through controlledtransfers of charge between capacitors in the circuit. A Dickson chargepump is an example of such a conversion circuit. Control of the chargetransfer between the capacitors generally makes use of circuit elementsthat act as “switches,” for example, diodes or FET transistors.

Some configurations of switch elements and capacitors limit the typicalmaximum voltage across the switch elements in normal operation. Suchlimited voltages permit use of switch elements that do not necessarilyhave to accommodate the full high side voltage or the difference betweenthe high side and the low side voltages, thereby permitting use “lowvoltage” elements. For example, in a conventional Dickson charge pumpperforming a conversion between 20 volts and 5 volts in 4 stages, switchelements typically experience a maximum of 10 volts in operation andtherefore require a rating (e.g., breakdown voltage rating) of 10 volts.

Charge pumps step up or step down an input voltage by storing a fractionof the input voltage across each capacitor. As the magnitude of thevoltage conversion increases, the number of capacitors requiredincreases. Switches on both terminals of each capacitor are necessary toperform the charge transfer, as well as configure the charge pump toprovide a desired voltage conversion ratio.

FIGS. 1A-1B show two charge pumps. The first in FIG. 1A is a 1:3step-down configuration and the second in FIG. 1B is a 3:1 step-upconfiguration. The voltage labels on each node have two values, one foreach stage of operation: voltage value during stage 1/voltage valueduring stage 2. Each switch needs to be turned on and off in anon-overlapping manner during stage 1 or stage 2. For either the step-upor step-down, the node labeled VX is the lowest charge pump voltagelevel: VX is typically the output of a step-down, and conversely theinput of a step-up. VX also sets the unit voltage drop across eachswitch when the switch is off: the switches at the bottom of thecapacitors each see a maximum voltage drop of VX, while the switches atthe top of each capacitor see a maximum voltage drop of 2VX. This meansthat the transistors selected as switches at the top of the capacitorsrequire a drain-to-source breakdown voltage (BV_(DSS)) above 2VX toavoid damage. In general the higher the BV_(DSS) of a MOS transistor,the larger the transistor area and capacitances for a givenon-resistance which increases die cost and switching power loss.Therefore, it is desirable to use a transistor whose BV_(DSS) is closeto the maximum voltage drop the transistor needs to support.

FIG. 2 shows an interleaved version of the step-down charge pump in FIG.1A where the switches at the top of each capacitor now see a maximumvoltage drop of only VX. It should be noted that the FIG. 2 interleavedtopology may reduce the maximum voltage drop seen across each switch, assimply cascoding each of the top switches (or using two series-connectedtransistors per top switch), although other approaches may also achievesthis purpose. For most CMOS processes, the efficiency and die area gainsfrom using the same low BV_(DSS) transistors are still advantageousenough to justify the higher transistor count and complexity. Thecomplexity arises from having to control and operate these low-voltagetransistors at various common-mode voltage multiples of VX. Referring toFIG. 2 as an example, the switch that connects the top-most capacitor toVIN at 6V can be a 3.3V transistor since the transistor sees 2Vdifferentially across its drain-to-source terminals when not conducting,despite the absolute voltage levels at the transistor drain and sourceterminals (4V or 6V depending on the stage of operation; 4V being thecommon-mode voltage level for this switch) exceeding 3.3V. This isbecause BV_(DSS) is a differential voltage constraint across thetransistor drain-to-source terminal, rather than an absolute constraintat each of the transistor terminals. Although the drain and sourceterminals each have an absolute breakdown voltage to the siliconsubstrate, these absolute breakdown voltages are typically much higherthan BV_(DSS) and therefore allow the transistor to be operated at acommon-mode voltage level above B_(VDSS).

In addition to BV_(DSS), another differential voltage constraint for aMOS transistor is the maximum gate-to-source voltage (V_(GSmax)) whichis determined by the gate-oxide breakdown voltage. Modern CMOS processeswith small geometries and low-voltage transistors require thinner gateoxides to maintain performance, which results in lower V_(GSmax) ratingsas well. This further complicates the design of a high voltageconversion ratio charge pump using low-voltage transistor switches,since care must be taken to avoid exceeding both gate-to-source anddrain-to-source voltage constraints during switch operation.

Commonly available low-voltage transistor flavors such as the 1.8V, 3.3Vand occasionally 5V transistors, usually specify a V_(GSmax) ratingequal to the maximum operating drain-to-source voltage rating,V_(DSmax), where V_(DSmax)<BV_(DSS). For applications where the minimumVX voltage in the operating range is sufficiently above the transistorthreshold voltage, it becomes practical and convenient to use the sameVX voltage level for the transistor gate drivers, instead of generatingseparate internal supply rails for this purpose. This is due to the factthat a VX-level voltage is already generated and supported between eachnon-switching node (e.g. VIN, VX, 4V node between the capacitors in FIG.2) in the interleaved charge pump, inherent to the charge pump operationitself. Therefore, the gate driver for each transistor can belevelshifted to the common-mode voltage level of that transistor, usethe same low-voltage transistors, and drive the transistorgate-to-source voltage between 0V and VX, as shown in FIG. 3. The nthsection of an interleaved charge pump showing a pair of switches at thetop of a capacitor, where n is an integer. An equivalenttransistor-level representation is shown on the right with the gatedrivers used to turn the transistors on and off. The transistors and thegate driver circuitry see a maximum of a VX voltage across them. Thehigh-side switch shown is a PMOS transistor, but can also be an NMOS ifits gate driver was bootstrapped between the capacitor node shown and anadjacent capacitor node that switches between V_(n+1) and V_(n+2)

Charge-pumps step-down or step up an input voltage by storing a portionor multiples of the input voltage across capacitors. As the magnitude ofthe transformation increases, the number of capacitors used increases.Each capacitor helps create a unique intermediate voltage during part ofthe operating cycle. The switches used to re-arrange the capacitors intodifferent configurations need to be powered by some energy source.

In FIGS. 4A-B, a series-parallel and a Dickson charge pump in a 1:5(step-down) configuration (or 5:1—step-up—if the power flow is reversed)are shown. The voltage labels on each node have two values: the first isthe voltage value during stage 1 of operation; the second is the voltagevalue during stage 2 of operation.

In a Dickson charge-pump, each stage sees only a small fraction of thetotal voltage at the high voltage side of the charge-pump. This allowsfor using lower voltage rated devices and improves efficiency. However,if the high-voltage side should suddenly step up rapidly, it is possiblefor the low-voltage switches to experience temporary over-voltage stressthat can result in damage.

In general, it is important to protect the switch elements from beingexposed to voltages in excess of their breakdown voltages to preventdamage to the conversion circuit or faulty operation of the circuit.

SUMMARY

In one aspect, in general, transient or fault conditions for a switchedcapacitor power converter are detected by measuring one or more ofinternal voltages and/or currents associated with switching elements(e.g., transistors) or phase nodes, or voltages or currents at terminalsof the converter, and based on these measurements detect that acondition has occurred when the measurements deviate from apredetermined range. Upon detection of the condition fault controlcircuitry alters operation of the converter, for example, by using ahigh voltage switch to electrically disconnect at least some of theswitching elements from one or more terminals of the converter, or byaltering timing characteristics of the phase signals.

In another aspect, in general, in the event that a capacitor isaccidentally shorted to the next stage, across itself, or to ground(such as its bottom plate to ground), an over-voltage and under-voltageprotection can be implemented. Each capacitor in the charge-pump ismonitored to see if it is within an acceptable range given thecharge-pump ratio. For example, if the output of the charge-pump shouldbe 2V, than the capacitor closest to the output should also beapproximately 2V. In adiabatic charging, the capacitor voltage can varyquite a bit during each cycle, so there needs to be sufficient margin inthe over and under voltage protection to account for normal voltagevariation.

In another aspect, in general, a switched capacitor power converter hasa first terminal for coupling to a first external circuit atsubstantially a high voltage, and a second terminal for coupling to asecond external circuit at substantially a low voltage lower than thehigh voltage. In operation of the power converter, charge passes on acharge transfer path between the first terminal and the second terminal.The converter includes a plurality of semiconductor switch elements.These switch elements include a first set of switch elements on thecharge transfer path between the first terminal and the second terminal,wherein no switch element in the first set of switch elements isconnected in series with either the first terminal or the secondterminal to carry substantially all the current passing through saidterminal, and wherein each switch element in the first set of switchelements is configured to form a controllable charge transfer pathbetween a corresponding subset of a plurality of capacitors. The switchelements also include a second set of switch elements configured to formelectrical connection of at least some of the capacitors to alternatingreference voltages. The plurality of switch elements is configured toform said interconnections in successive states in operation. Theconverter further includes measurement circuitry configured to measure avoltage and/or a current characteristic of one or more switch elementsof the first set of switch elements or the second set of switchelements, and fault control circuitry coupled to the measurementcircuitry configured to alter operation of the power converter upondetection of a condition determined when the measured characteristics ofthe switch elements deviate from a predetermined range of saidcharacteristics.

Aspects can include one or more of the following features.

The plurality of switch elements further includes a third set of switchelements on the charge transfer path between the first terminal and thesecond terminal connected in series with either the first terminal orthe second terminal.

The second set of switch elements include switch elements that formelectrical connection of at least some of the capacitors to the lowvoltage terminal during some states of operation (e.g., at “phase nodes”of the converter).

The stages of operation comprise a repeated sequence of clocked stages.

The converter further comprises the plurality of capacitors, with eachcapacitor having a terminal coupled to a terminal of at least one switchelement of the plurality of switch elements. In some examples, thecapacitors and switch elements are integrated in a monolithic device.

The converter comprises a Dickson charge pump.

The voltage and/or current characteristics of the one or more switchelements belong to a group consisting of:

-   -   a voltage across terminals of a switch element of the first set        of switch elements;    -   a current through a switch element of the first set of switch        elements;    -   a voltage at a junction between a switch element of the first        set of switch elements and a capacitor of the plurality of        capacitors;    -   a voltage across terminals of a capacitor of the plurality of        capacitors coupled to the switch element;    -   a voltage at a junction between a switch element of the second        set of switch elements and a capacitor of the plurality of        capacitors; and    -   a current through a switch element of the first set of switch        elements.

The voltage and/or current characteristic of the switch elementcomprises a voltage across terminals of the switch element.

The voltage and/or current characteristic of the switch elementcomprises a current through the switch element.

The voltage and/or current characteristic of the switch elementcomprises a voltage at a terminal of the switch element.

The voltage and/or current characteristic of the switch elementcomprises a voltage across terminals of a capacitor of the plurality ofcapacitors coupled to the switch element.

The switch elements of the second set of switch elements form a phasegenerator, and wherein the voltage and/or current characteristic of theswitch element comprises a voltage and/or current supplied by the phasegenerator.

Each of the semiconductor switch elements comprises a FET transistor forcoupling at least two of the capacitors.

At least some of the semiconductor switch elements comprise a network ofmultiple FET transistors.

At least some of the switch elements of the first set of switch elementsor the second set of switch elements have a maximum voltage rating lessthan the high voltage.

At least some of the switch elements of the first set of switch elementsor the second set of switch elements have a maximum voltage rating lessthan the difference between the high voltage and the low voltage.

At least some of the switch elements of the first set of switch elementsor the second set of switch elements have a maximum voltage rating nogreater than a fraction 1/N, N>1, of the difference between the highvoltage and the low voltage.

The fault control circuitry comprises one or more switches each havingmaximum voltage rating greater than the voltage rating of at least someof the plurality of switches, the one or more switches being configuredto electrically disconnecting or limit current flow through at leastsome switch elements of the plurality of switch elements. In someexamples, the one or more switches comprise a switch coupled directly tothe first terminal. In some examples, the one or more switches comprisea switch coupled between two switch elements of the plurality of switchelements.

The fault control circuitry is configured to modify the characteristicsof the phases upon detection of the condition. In some examples, thecharacteristics of the phases belong to a group consisting of:

-   -   a duty cycle of clocked phases;    -   a clocking frequency of the phases; and    -   a skipping of one or more clock cycles of clocked phases.

DESCRIPTION OF DRAWINGS

FIGS. 1A and 1B are schematics of a 1:3 voltage conversion ratio(step-down) charge pump a 3:1 voltage conversion ratio (step-up) chargepump, respectively.

FIG. 2 is a schematic of an interleaved version of the step-down chargepump in FIG. 1A.

FIG. 3 is a schematic of a transistor-level representation of a pair ofswitches.

FIGS. 4A-B are schematics of a series-parallel and a Dickson chargepump, respectively.

FIG. 5 is a schematics of fault indicator circuit.

FIG. 6 is a schematic of charge pump with a fault detection circuit.

FIG. 7 is a schematic of charge pump with cascoded switches.

FIG. 8 is a schematic of charge pump with cascoded switches anddetection circuitry.

FIG. 9 is a schematic of a charge pump with input control.

FIG. 10 is a schematic of a charge pump with input disconnect.

FIGS. 11A-B are schematics of high-side and low-side switches for astep-down and a step-up, respectively.

FIGS. 12A-B are schematics of current sensing circuits.

FIG. 13 is a schematic of a fault detector with a charge pump as shownin FIG. 1A.

FIGS. 14-15 are schematics to current sensing and comparator circuitssuitable for use in the circuit of FIG. 13.

FIG. 16 is a schematic including a step-down charge pump with faultdetection circuitry.

FIGS. 17-20 are a schematics each including a missing or open terminalfault detector.

DESCRIPTION 1 Overview

A number of related approaches are described below for detection offaults (or potential faults or potential failures, exceeding deviceratings, etc.) of switched capacitor power converters and/or circuitrycoupled to such converters (e.g., load circuitry), and in some casesapproaches for controlling operation of converters after detection ofsuch faults, for example, to avoid failure within and external to thecharge pump. These faults or failures may occur in operation, or in ashut-down (i.e., not actively operating as a power converter) butpowered state. Note that the approaches described below may be usedindependently, and in general, may be used together in variouscombinations. Furthermore, it should be understood that althoughapproaches described below may be illustrated in the context of aparticular type of converter (e.g., a series/parallel or a Dickson), atleast some of the approaches are applicable to a much wider range ofconverters.

A number of the approaches described below differ according to what ismeasured, and according to how the fault or failure is mitigated.Measurements can include one or more of

-   -   voltage across the source and drain of a switching transistor    -   current through a switching transistor;    -   voltage at a terminal of a capacitor of the converter (e.g., at        the terminal of a device to which an external capacitor is        attached, at a terminal of a switching transistor is attached,        etc.)    -   voltage and/or current at the high voltage or low voltage        terminal of the converter    -   voltage and/or current at the output of a phase node, or at a        terminal of a capacitor attached to a phase node        Approaches to mitigating the fault or failure can include one or        more of:    -   Suspending operation of the converter (e.g., suspending the        clocked operation);    -   Modifying the clocking of the converter without suspending        operation, for example, by increasing or slowing the clocking        rate, changing the duty cycle, etc. to permit voltage        equilibration within the converter, inhibiting all switching;    -   Restarting the converter (e.g., executing a startup operation        sequence);    -   Controlling a high-voltage switch (transistor) at the        high-voltage terminal of the converter, for example, to limit        current flow through the converter (e.g., by opening the switch        to stop current flow, or putting the switch in a constant        current mode);    -   Decoupling the electrical path(s) through the converter with one        or more switches (e.g., high-voltage switches), which may be on        internal paths in the converter;    -   Generating a logic fault indicator that causes a pin transition        or external interrupt signal so that the user is notified and        can take corrective action (e.g. reducing the external load,        suspending converter operation)    -   Changing the logic state of one or more bits in an internal        register, according to the type of fault(s) detected, to assist        the user in debugging the faults when the contents of this        internal register are read back

In the discussion below, FET transistors are used as examples ofsemiconductor switch elements. Other types of devices (e.g., other typesof transistors), and networks of multiple devices (e.g., series and/orparallel connections of transistors) can be used to form such switches.

Note that in some implementations, the converter may include a number ofparallel converters operating out of phase with one another (e.g, twoparallel converters 180 degrees out of phase, three converters 120degrees out of phase with overlapping phases, etc.), and the detectionand mitigation approaches may be performed independently for each phase,or can be coordinated. For example, during a recovery/restart of one ofthe parallel converters, the other converters may be reconfigured tooperate in a manner to provide uninterrupted power conversion (e.g., bysuitably adjusting their relative phase, over clocking rate, etc.).

2 Over/Under Voltage Sensing at Terminals

As introduced above, one approach generally uses sensed voltages at theterminals of the converter to detect over- or under-voltage conditions.In a number of embodiments, the charge pump is configured to preventcharge pump operation under atypical or fault conditions that would

a) exceed the V_(GSmax) and V_(DSmax) rating of the switchingtransistors, their gate drivers and associated control circuitryb) operate the transistors in a weak state where functional orparametric misbehavior can occurc) cause a subsystem connected in series with VX to operate outside ofthe normal range

If event (a) occurs, the damage to the charge pump can be immediate orlong-term whereby the part may continue to operate but at a reducedrobustness and performance level. Events (b) and (c) can cause abnormaloperating behavior, which can also degrade part robustness andperformance. Such events can occur since VX is likely to be a packagepin, thereby exposed and vulnerable to physical contact by the user.Furthermore, the assembly process itself may cause shorts or opens tooccur on a package pin or external component, or create shorts betweenadjacent pins or components. For instance, a user probing various nodeson the package or board while operating a step-down charge pump mayinadvertently short VX to ground or to a supply rail. Or the user mayunintentionally apply a larger than specified load current on VX,causing the VX voltage to drop below the normal operating range. Whenthe capacitors are external to the charge pump die and package, anassembly process defect may leave out a capacitor or leave open one ofthe capacitor connections to the charge pump. If the charge pump wasoperated with a missing or open capacitor, the VX voltage would alsodrop.

In applications where the charge pump is operated in series with anothersubsystem such as an LDO or another switching converter (inductor- orcapacitor-based), VX can either be the input that powers this subsystemor the subsystem output that powers the charge pump. In both cases, anunder-voltage or over-voltage event at VX may be undesirable for theperformance and robustness of the subsystem as well.

2.1 VX Under-Voltage and Over-Voltage Sensing and Lockout

In some embodiments the VX voltage is sensed during operation or in theshutdown-but-powered state, and an internal indicator is generated bycircuitry in or associated with the charge pump to disable operation orprevent charge pump operation upon enable (lockout), whenever the VXvoltage moves outside a predefined voltage window. When VX drops belowthe lower limit of the window, VX is under-voltage while VX isover-voltage when VX rises above the upper limit of the window. VXunder-voltage (UVLO) and over-voltage (OVLO) sensing and lockoutimplements a first-order protection of the low-voltage transistors usedin a high voltage conversion ratio charge pump, by preventing chargepump operation if the transistor absolute maximum voltage ratings areexceeded or if the transistor cannot switch reliably due to insufficientgate drive.

The OVLO threshold, or the upper limit of the VX-sensing window, shouldbe set above the maximum operating VX level required by the applicationbut below the V_(DSmax) rating of the transistors, to give margin fortolerances in the OVLO circuit and VX voltage transients. The UVLOthreshold, or the lower limit of the VX-sensing window, is set, forexample, below the minimum operating VX level including the largest VXripple amplitude that would occur across the application space, butabove the level where basic transistor functionality would fail ordegrade to a point that would adversely affect the performance of thecharge pump and/or the subsystem connected in series with VX. Examplesof the latter constraint are the voltage at which the gate driver outputfails to transition according to the gate driver input, or where thegate driver's propagation delay increases to an extent that would causemisbehavior elsewhere in the charge pump. Depending on the applicationspace, there is usually more flexibility in setting the UVLO thresholdversus the OVLO threshold, since the latter is constrained mainly by thevoltage rating of the charge pump transistors. Instead of a fixedvoltage level, the UVLO threshold can be variable as a function of theVX voltage level and the VX ripple amplitude, if such information wasavailable to the charge pump through sensed inputs or internallyprogrammed settings. For instance, the charge pump switching frequencyand capacitor values could be internally programmed settings and thesesettings directly govern the VX ripple amplitude.

FIG. 5 shows a circuit example that implement UVLO and OVLO sensing atthe VX node. The example uses two comparators whose outputs are combinedby an OR gate to generate a logical fault indicator. The inputs to thecomparators are VX or some fraction of VX generated using an internalvoltage divider, and the thresholds V_(THuvlo) and V_(THovlo), which arescaled from the UVLO and OVLO threshold by the same fraction as theVX-based input to the comparator. For all practical purposes,V_(THovlo)>V_(THuvlo). When the VX voltage lies in between the UVLO andOVLO thresholds, the outputs of the comparators are both low andtherefore the fault indicator is also a logic low. Otherwise the faultindicator will be a logic high and this logic state can be used todisable charge pump operation or enable.

Note that while most of the charge pump illustrations above are for astep-down configuration, this approach can also be applied in similarfashion to step-up configurations, since the one is a reverse-directionpower flow version of the other.

3 Detection of Internal Voltage Deviations

Another approach detects deviations of voltage on capacitors in theconverter outside their expected operating ranges.

3.1 Detection Scheme 1

FIG. 6 shows the basic technique applied to the detection of a faultcondition on capacitor C1. A similar circuit is needed to monitor thevoltages on C2, C3 and C4. This example shows a 5:1 step-down Dicksoncharge pump, but can be similarly applied, as other examples, to astep-up configuration, to all possible charge pump ratios and to theSeries-Parallel charge pump topology.

The charge pump operates in a substantially conventional manner, withthe addition of PMOS device MP1 (which has to be selected to operate atthe higher voltage across C1), together with resistors R1 and R2 as wellas switch S10 and comparators CMP1 and CMP2.

Current I1 is roughly proportional to the voltage across C1 (the erroris the source-gate voltage of MP1). Current I2 is very nearly identicalto I1. By proper selection of R2 the voltage across this resistor is,roughly, an analog of the voltage across C1 and can be scaled asdesired. Switch S10, along with capacitor Cfilter, is used to allowdetection of the voltage on R2 only when switch S8 is on (switch S9forces the R2 voltage to be 0). CMP1 and CMP2, along with the UnderVoltage and Over Voltage reference voltages form what is called a windowcomparator. Either the OV or UV outputs being asserted indicates a faultcondition which then triggers one or several of the protectionmechanisms implemented.

3.2 Detection Scheme 2

FIG. 7 shows a possibly more practical embodiment of the 5:1 Dicksoncharge pump. The additional switches are required because, withreference to the figure FIG. 6—switches S2, S3 and S4 are exposed, whenin the off state, to twice the voltage across switches S1 and S5 in theoff state.

For a given charge pump ratio and a fixed VIN, annotated voltages V1, V2and V3 do not change appreciably. FIG. 8 shows a detection scheme thatrelies on detecting a large change in voltage across the charge pumpcaps by means of a window comparator for each capacitor (previouslydescribed above). The input to this window comparator is an attenuatedversion of the charge pump capacitor voltages themselves. Resistorratios R1/R2, R3/R4 and R5/R6 are chosen so as to appropriately scalethose capacitor voltages. Comparator output signals OV_(—) and UV_(—)can be used to trigger any or all of the protection mechanisms beingimplemented.

4 High-Side Transient Protection

Referring to FIG. 9, another way of protecting from a transient fault isto use a high-voltage disconnect (SWINP) switch that performs as avoltage or current limiting device during a transient event. The methodimplemented in the circuit of FIG. 9 controls the SWINP switch with oneor a combination of several modes of operation.

-   -   One possible mode is as a Low Drop Out (LDO) regulator.    -   A second mode is a Current Limited (CL) switch.    -   A third mode is a Transient Voltage Suppressor (TVS).

In LDO mode the voltage at N1 has a maximum value. The CONTROL does notallow voltage on N1 to exceed the maximum voltage that the charge-pumpcan sustain. In the condition where VIN is less than the maximum voltagethe switch SWINP would be in a low impedance state. For example themaximum allowed voltage on N1 is 22 volts. In normal operation thevoltage on VIN is 20 volts. The voltage on N1 is almost 20 volts. TheVIN supply rises to 22 volts. The voltage on N1 remains at 20 volts.

In CL mode there is a maximum current that SWINP will allow to passthrough from VIN to N1. In the condition where N1 is at or below themaximum voltage set by the LDO, the output current of SWINP is limited.For example in normal operation VIN=16 volts and voltage on N1 is almost16 volts. The current through SWINP is <1 ampere. A situation ariseswhere the current through SWINP would need to supply 3 amperes tomaintain node N1 at 16 volts. This 3 amperes is above the safe operatingrange on the switches. The CONTROL would limit the SWINP current to 2amperes and the voltage on N1 would decrease. Note that this mode isalso useful to indirectly mitigate the effect of transient voltages onthe terminals.

In TVS mode the voltage on N1 is not allowed to change by more than apredefined rate. The voltage on N1 is below the maximum allowed by theLDO, the current is below the maximum allowed by CL. The TVS will allowthe charge-pump to redistribute the voltage from N1 appropriately on thecapacitors C_. For example in normal operation VIN=16 volts. The currentthrough SWINP is <1 ampere. A situation arises where the voltage on VINrises to 18 volts in 10⁻⁶ seconds (1 μs). The maximum voltage slew rateon N1 is designed to be 0.100 volts per μs. The voltage on N1 will riseto 18 volts, but the CONTROL would make it take 20 us to reach this newvoltage level on N1.

4.1 High-Side Protection

In a conventional Dickson Charge-pump (see, e.g., FIG. 4B), each stagesees only a small fraction of the total voltage at the high voltage side(VIN) of the charge-pump. In steady state operation the voltage acrossany of SW_(—) does not exceed VOUT. This allows for using lower voltagerated switches and improves efficiency.

Prior to power being applied to the circuit all nodes are at zero volts(GND) potential. When a voltage VIN is first applied to the circuit, thevoltage across the capacitors C1, C2, C3, C4 is still zero volts. Thisrequires the switch SW4 to be designed to support the full voltage ofVIN.

The switches SW_ are all regularly toggled between a low impedance stateand a high impedance state in a predefined sequence. Each switch SW_ hasa gate capacitance. The charging and discharging of the gate capacitanceis a power loss. When a switch is toggled there is a finite power loss.This power loss reduces the efficiency of the charge-pump. The powerloss is dependent on the switch design.

A higher voltage rated switch will typically have much larger gatecapacitance. The toggling power loss of a high voltage designed switchis significantly larger than the power loss from a low voltage designedswitch of the same low impedance value.

It is advantageous to use an additional disconnect switch (SWINP) on thehigh-voltage side that is designed for high voltages, as shown in FIG.10. Since this switch doesn't toggle periodically when the charge-pumpis operating, its large gate capacitance doesn't affect performance.

During powerup the switch SWINP is able to manage the voltages appliedto the remaining switches. The voltage on N1 is managed such that thecapacitors C_(—) can approach steady state voltages without overstressing the switches SW_. This allows the remaining switches to allremain low voltage designed switches.

There are several possible faults for a charge-pump power converter.Faults include both internal and external devices. Faults can occurprior to power being applied or during powered operation. A capacitorcan become an electrical open or any two nodes can be electricallyshorted. Common faults include assembly errors with too much orinsufficient solder at the printed circuit board connections. When afault does occur, this SWINP switch can then current limit or disconnectthe high-voltage side from the charge-pump and help protect it fromdamaging current levels.

5 Phase Node Monitoring

A number of further approaches make use of monitoring current at thephase nodes of the converter.

Embodiments of such n approaches are described below and provide anefficient way to detect the numerous types of fault events that mayaffect both the charge pump and its capacitors. The detected faultevents include phase node shorted to a fixed rail (ground or phase-pumpsupply); positive terminal of a capacitor shorted to a fixed rail(ground or input voltage VIN) or charge pump output voltage VOUT;positive terminal of a first capacitor shorted to the positive terminalof a second capacitor (the first capacitor being closest to inputvoltage VIN); missing capacitor or open capacitor terminal; and chargepump output shorted to ground or output over-current.

These fault events are most likely to occur when the charge pump usesexternal or non-integrated capacitors, since these components and theirconnections are exposed and vulnerable to physical contact by the user.Furthermore, the assembly process itself may cause shorts or opens tooccur on a pin or component, or create shorts between adjacent pins orcomponents. The fault events can either occur during start-up or normaloperation.

Embodiments described below rely at least in part on the recognitionthat an extensive fault coverage for charge pumps in an efficient way(in terms of die area, quiescent current) can be achieved by sensing thecurrent in the charge pump phase nodes. By sensing the current flowthrough each switch while the switch conducts, a fault event can bedetected based on the switch current magnitude and polarity.

It is also possible to detect some of the aforementioned fault events bysensing the current through the input voltage VIN or through theswitches at the positive terminal of each capacitor. However, the inputvoltage VIN and the positive terminals of each capacitor can operate ata high voltage depending on the charge pump configuration, therebyrequiring the current-sense circuit to be designed using high-voltagedevices or be powered between high-voltage rails.

Designing for high-voltage operation typically requires more die areaand more quiescent current, compared to an equivalent circuit that ispowered from the lowest charge pump voltage level, as would be used inthe approach described here. Furthermore, this method can result insignificantly higher die area and quiescent current savings when thephase nodes common to an operating state are shared since there wouldonly be two phase nodes per charge pump, compared to current sensing atthe switches of each capacitor's positive terminal where no node or pinsharing is possible. However, such sharing is not essential (e.g., witha separate phase node for each capacitor) to obtain the benefit of theapproach.

FIG. 11A defines the current flow polarity through the high-side andlow-side switches for a step-down charge pump. Similarly, FIG. 11Bdefines the current flow polarity through the high-side and low-sideswitches for a step-up charge pump. The current flow polarity duringnormal operation is illustrated by the solid arrows, while the reversecurrent flow polarity that may occur upon a fault event is illustratedby the dashed arrows.

For some fault events, the conducting high-side or low-side switch seesonly an atypical increase in the current magnitude compared to themagnitude in the absence of a fault. In other events, the conductinghigh-side or low-side switch sees both a reversal in the polarity ofcurrent flow and an increase in current magnitude. Since the state ofevery switch (conducting or not) in the charge pump is always known andwell-controlled, it is not difficult to compare the switch currentmagnitude and/or polarity to a predefined level that signals a validfault event. This predefined level can be fixed for all operatingconditions of the charge pump, user-programmable or track specificsignals like output load current, if such information were available tothe charge pump. Upon the detection of the fault event, part damage or a“smoke-and-fire” occurrence can be prevented by immediately turning offall phase node switches and letting the phase nodes go high-impedance.Note that for protection against some types of faults, the switchescontrolling the phase nodes have to have a high voltage rating.

TABLE 1 summarizes the current flow polarity through the high-side andlow-side switches of a step-down charge pump for the following faultevents: A phase node shorted to ground, a phase node shorted tophase-pump supply, a positive terminal of a capacitor shorted to ground,a positive terminal of a capacitor shorted to the input voltage VIN, apositive terminal of a capacitor shorted to the output voltage VOUT, apositive terminal of a first capacitor shorted to a positive terminal ofa second capacitor, and charge pump output shorted to ground or outputover-current. For a step-up charge pump, the high-side and low-sideswitch current flow polarity would be the inverse of the step-down,except for the fault events denoted with an asterix.

TABLE 1 High-side Low-side Switch Switch Current Flow Current Flow FaultEvent Polarity Polarity (a) A phase node shorted to ground Reverse N/A(b) A phase node shorted to phase-pump N/A Reverse supply (c) A positiveterminal of a capacitor Reverse Normal shorted to ground (d) A positiveterminal of a capacitor Normal Reverse shorted to the input voltage VIN*(e) A positive terminal of a capacitor Reverse Normal shorted to theoutput voltage VOUT* (f) A positive terminal of the first Normal Reversecapacitor shorted to the positive terminal of the second capacitor* (g)Missing capacitor or open capacitor Normal Normal terminal (h) Chargepump output shorted to Normal Normal ground or output over-current

With the exception of an output over-current, the faults listed in TABLE1 are much less likely to occur when the capacitors are integrated onthe same die as the charge pump, connected to the charge pump die usinga through-silicon via process, or consist of discrete componentsco-packaged on top of the charge pump die within a single module.However, having fault detection can still be useful as a diagnostic toolor for preventing smoke-and-fire events when process defects (e.g. metalshorts or opens between adjacent on-chip capacitors) or co-packagingerrors occur.

FIGS. 12A-B illustrate two circuits that can be used to perform switchcurrent sensing. Both circuits utilize a transconductance amplifier GM1to convert a voltage drop across either a switch or a sense resistor inseries with the switch into a sense current ISEN, whose magnitude isproportional to the switch current ISW. The polarity of sense currentISEN in and out of the amplifier GM1 follows the polarity of the switchcurrent ISW. The sense current ISEN can then be directly compared with acurrent whose magnitude and polarity are consistent with the fault eventto be detected, to generate a logic-level output fault indicator.

For example, if the transconductance of amplifier GM1 in FIG. 12A isdesigned to be directly proportional to the switch conductance, then thesense current ISEN can be a direct multiple of the switch current ISWand no other variable to a first order. Alternatively in FIG. 12B, thesense resistor in series with the switch can consist of the metalinterconnect between the switch and the package pins, which can be onthe same order of magnitude as the switch on-resistance.

FIG. 13 shows how an example of the fault detector can be coupled withthe charge pump in FIG. 1A. Across each of the four switches at thephase nodes P1 and P2 is a current sensing and comparator circuit: CS1senses the high-side switch current at phase node P1, CS2 senses thehigh-side switch current at phase node P2, CS3 senses the low-sideswitch current at phase node P1, and CS4 senses the low-side switchcurrent at phase node P2. Each of the four current sensing andcomparator circuits has a logic output that is a logic-low when no faultis detected, and a logic-high when a fault is detected based on theswitch current magnitude and polarity changes. If any one or more of thefour current sensing and comparator circuits CS1 to CS4 has a logic-highoutput in the middle of charge pump operation, a logic gate OR1 willoutput a logic-high signal that sets a set-reset latch SR1, therebygenerating a latched logic signal that can be used to close allswitches, shut down the charge pump immediately and generate a businterrupt or toggle an output fault indicator pin. The charge pump thenremains in shutdown until a fault reset signal is received by theset-reset latch SR1, at which point charge pump operation can resume.The fault reset signal can come from a supply undervoltage-lockout or atoggle on the charge pump enable input.

FIGS. 14 and 15 illustrate two circuits that implement the currentsensing and comparator circuit in FIG. 13, where the same implementationcan apply to all four current sensing and comparator circuits CS1 toCS4. The current sensing portion of FIGS. 14-15 can be implemented usingeither the circuit in FIG. 12A or FIG. 12B, though only the circuit inFIG. 12A is shown. In FIG. 14, the sense current ISEN whose magnitudeand polarity follows the switch current is mirrored into three separatecurrents ISEN1 to ISEN3 using a current mirror or a current amplifier,each equaling the sense current ISEN or its multiple. The currents ISEN1and ISEN2 can be individually converted into voltages VSEN1 and VSEN2using resistors, which are then compared against threshold voltages VTH1and VTH2 using voltage comparators CP1 and CP2 respectively. The currentISEN3 is fed into a single-ended current comparator ICP1 (such as aTraff current comparator) used to determine current polarity: when theswitch current polarity is normal, the sense current ISEN flows out ofthe transconductance amplifier GM2 and the mirrored current ISEN3 flowsinto the single-ended current comparator ICP1 input terminal, causingthe output voltage of ICP1 to be a logic-low; conversely when the switchcurrent polarity reverses upon a fault event, the sense current ISENalso reverses polarity and the mirrored current ISEN3 flows out of thesingle-ended current comparator ICP1 input terminal, causing the outputvoltage of ICP1 to be a logic-high. The voltage comparators CP1 and CP2are used to determine whether the magnitude of the normal polarityswitch current exceeds a level consistent with a fault event. Differentfault events can be associated with different switch current magnitudes,and can be detected and differentiated by using more than one comparatorinput voltage threshold (VTH1≠VTH2). The outputs of voltage comparatorsCP1, CP2 and ICP1 are combined in a logical OR operation by the logicgate OR2 to generate a logical fault indicator that is logic-highwhenever any one or more of the comparator outputs are logic-high. Itshould be noted that the comparators CP1 and CP2 do not have to bevoltage comparators, but can also be differential current comparators,in which case the resistors are no longer needed and the voltagethresholds VTH1 and VTH2 should be replaced with current thresholdlevels consistent with each fault event to be detected.

FIG. 15 shows an alternate implementation of the current sensing andcomparator circuit in FIG. 4A, where instead of using a single-endedcurrent comparator like ICP1 in FIG. 4B to sense a reversal in switchcurrent polarity, a voltage comparator CP3 similar to voltagecomparators CP1 and CP2 is used. The sense current ISEN is fed into aresistor divider network powered off a reference voltage, VREF, while acommon voltage tap off the resistor divider network, VSEN, is comparedby three voltage comparators CP1 to CP3. The magnitude of the voltagetap VSEN is a function of both the magnitude and polarity of the sensecurrent ISEN: when the switch current polarity is normal, the sensecurrent ISEN flows out of the transconductance amplifier GM2 and intothe resistor divider network at the voltage tap point VSEN, therebyincreasing the magnitude of VSEN above the level defined as VDIV thatwould ordinarily be determined by the value of the resistor dividerratio and the reference voltage, VREF. Therefore, the threshold voltagesVTH1 and VTH2, which correspond to fault events where the switch currentmagnitude is atypically elevated, should be set above VDIV. Upon a faultevent where the switch current polarity reverses, the sense current ISENflows into the transconductance amplifier GM2 output, pulling thevoltage tap VSEN below VDIV. Consequently, the threshold voltage VTH3should be set below VDIV. Like FIG. 4B, the outputs of voltagecomparators CP1 to CP3 are combined in a logical OR operation by thelogic gate OR2 to generate a logical fault indicator that is logic-highwhenever any one or more of the comparator outputs are logic-high.

A missing capacitor or open capacitor terminal fault event typicallydoes not result in immediate charge pump damage or a smoke-and-fireevent. Nevertheless, it is desirable to detect this fault occurrence andtake preventive measures such as shutting down the charge pump,otherwise the charge pump will continue to operate for several cyclesbefore eventually exceeding specified tolerances.

FIG. 16 illustrates a step-down charge pump 50 with fault detectioncircuitry to detect an outer capacitor open terminal connection in themiddle of operation. An outer capacitor is defined herein as thecapacitor closest to the input voltage YIN or the output voltage VOUT.Whenever a charge pump has two or fewer capacitors as shown in FIGS.1A-1B, all the capacitors are outer capacitors.

Charge pump 50 has N capacitors, C₁ to C_(N), where N is an even integernumber. The odd-numbered capacitors C₁, C₃, . . . C_(N-1) share a firstphase node P1 and the even-numbered capacitors C₂, C₄, . . . C_(N) sharea second phase node P2. The first and second high-side switches HS1, HS2couple the first and second phase nodes P1, P2 to the output voltageVOUT, respectively. Similarly, the first and second low-side switchesLS1, LS2 couple the first and second phase nodes P1, P2 to ground,respectively. In this example, the outer capacitors are C₁ and C_(N).The load at the charge pump 50 output is a current source IOUT, whichenables the charge transfer between the capacitors to take place via asmooth and steady charging current proportional to IOUT, in a processdescribed as soft charging.

During normal steady-state operation with soft charging, the currentsthrough the conducting phase switches in each state are equal inmagnitude. For instance in a first state, the first high-side switch HS1and the second low-side switch LS2 conduct current wherein both switchescarry the same magnitude of current. Likewise in a second state, thesecond high-side switch HS2 and the first low-side switch LS1 conductcurrent wherein both switches carry the same magnitude of current.

If one terminal of either outer capacitor C₁ or C_(N) is disconnected inthe middle of operation, the following occurs for several switchingcycles before the charge pump output eventually collapses: the phasenode currents become unbalanced in every other state or the currentmagnitude through one conducting high-side switch no longer matches thecurrent magnitude through the other simultaneously conducting low-sideswitch. This fault can then be detected by simultaneously sensing andcomparing the phase node switch currents during each state, andgenerating a logic flag whenever the current magnitudes becomemismatched by more than a predefined offset. To avoid false positives,this logic flag should be set only if the current mismatch exceeds thepredefined offset in at least multiple consecutive cycles, and thepredefined offset should be large enough to ignore non-fault mismatchesthat can arise from mismatches in the outer capacitor values.

FIG. 16 also shows four current sensing and comparator circuits, CS5,CS6, CS7, CS8; each across one of the four phase switches. Theparticular implementation of each current sensing and comparator circuitis similar to that in FIG. 14 or FIG. 15. To detect a mismatch betweenthe high-side and low-side switch currents in each state, one of theFIG. 14 or FIG. 15 voltage thresholds VTH1 or VTH2 can be designed to bea function of the switch current in that state. For example in the firststate when the first high-side switch HS1 and the second low-side switchLS2 conduct, the voltage threshold VTH1 in the current sensing andcomparator circuit CS5 should be proportional to the current magnitudeof the low-side switch LS2, in order to sense the current mismatchmagnitude between high-side switch HS1 and low-side switch LS2.Similarly in the second state when the second high-side switch HS2 andthe first low-side switch LS1 conduct, the voltage threshold VTH1 in thecurrent sensing and comparator circuit CS6 should be proportional to thecurrent magnitude of the low-side switch LS1, in order to sense thecurrent mismatch magnitude between high-side switch HS2 and low-sideswitch LS1. The proportion of the phase switch current magnitude used togenerate the voltage threshold VTH1 determines the predefined offset bywhich an open outer capacitor terminal fault can be detected anddifferentiated from non-fault mismatches. In addition, the comparatorCP1 should have a symmetrical input offset or hysteresis, or be a windowcomparator in order to detect a bidirectional current mismatch.

An example of a missing or open capacitor terminal fault detector canalso be applied to a charge pump where the phase nodes and switches arenot shared by the common-state capacitors, such as charge pump 60A shownin FIG. 17. Like charge pump 50A, there are N capacitors, C₁ to C_(N),in charge pump 60A where N is an even integer number. Each capacitor hasits own pair of phase switches that connect the capacitor negativeterminal between ground and the output voltage VOUT. There arealtogether N high-side switches and N low-side switches, instead of just2 high-side switches and 2 low-side switches for the charge pumps inFIGS. 13 and 16. Across each phase switch is a current sensing circuit,shown in FIG. 17 as HCS₁ to HCS_(N) for the high-side switches and LCS₁to LCS_(N) for the low-side switches. The phase node current sensingscheme now applies to a greater number of switches at the expense of diearea and quiescent current, but provides much more information on thecurrent through each capacitor and wider fault coverage. In this case,an open capacitor terminal fault can be detected in any of thecapacitors, not just the outer capacitors, by flagging a per-capacitorcurrent level that is practically zero or significantly lower than thatof the other capacitor current levels.

FIG. 18 shows a particular implementation of the fault detector for thehigh-side switches in FIG. 17. The current sensing circuit across eachphase switch can be implemented using the circuits in either FIG. 12A orFIG. 12B. As previously described, the output of each current sensingcircuit is a current that represents the magnitude and polarity of thecorresponding switch current. In FIG. 18, the current output of thefirst high-side switch current sensing circuit HCS₁ is first replicatedinto two current copies, ISEN_(HA1) and ISEN_(HB1), using a currentmirror or a current amplifier. The remaining current outputs of theodd-numbered high-side switch current sensing circuits HCS₃, HCS₅ . . .HCS_(N-1) are summed together with ISEN_(HA1) to generate a totalhigh-side switch current for the first state, ISEN_(H) _(—) _(STATE1),that is equivalent to the high-side switch HS1 current in FIG. 16.ISEN_(H) _(—) _(STATE1) can then be replicated using a second currentmirror or current amplifier to implement the comparator schemespreviously described in FIGS. 4B-4C to sense fault events that cause aswitch current magnitude and polarity change. ISEN_(HB1) is used todetect a missing or open terminal fault at capacitor C₁ since thecurrent magnitude through the first high-side switch and by extensionthat of ISEN_(HB1) will decrease to zero upon the fault: by connectingISEN_(HB1) to the input of a current comparator ICP3, the comparatoroutput logic level will be high if ISEN_(HB1) is detected to be close tozero, and low if ISEN_(HB1) is on the same order of magnitude as theother current outputs ISEN_(H1), ISEN_(H3), ISEN_(H5) . . . ISEN_(HN-1).

Similarly in the second state, FIG. 18 shows the current outputs of theeven-numbered high-side switch current sensing circuits HCS₂, HCS₄ . . .HCS_(N) summed together to generate a total high-side switch current forthe second state ISEN_(H) _(—) _(STATE2), that is equivalent to thehigh-side switch HS2 current in FIG. 16. The resulting fault detectionimplementation using ISEN_(H) _(—) _(STATE2) is then similar to thatused for ISEN_(H) _(—) _(STATE1), and the individual logic fault signalsfor each state can be logically combined in an OR operation.

FIG. 19 shows a particular implementation of the fault detector for thelow-side switches in FIG. 17. The current outputs of the even-numberedlow-side switch current sensing circuits LCS₂, LCS₄, LCS₆, . . . LCS_(N)are first replicated into two copies using a current mirror or a currentamplifier during the first state. During the second state, the currentoutputs of the odd-numbered high-side switch current sensing circuitsLCS₁, LCS₃, LCS₅ . . . LCS_(N-1) are similarly replicated using acurrent mirror or a current amplifier. For either state of operation,the first set of copied currents corresponding to each state(ISEN_(LA2), ISEN_(LA4), ISEN_(LA6) . . . ISEN_(LAN) in the first state;ISEN_(LA1), ISEN_(LA3), ISEN_(LA5) . . . ISEN_(LAN-1) in the secondstate) are summed together to generate a total low-side switch current,ISEN_(L) _(—) _(STATE1) and ISEN_(L) _(—) _(STATE2), that is equivalentto the current in the FIG. 5 low-side switches LS2 and LS1 respectively.The comparator schemes previously described in FIGS. 14-15 can then beapplied using ISEN_(L) _(—) _(STATE1) and ISEN_(L) _(—) _(STATE2).

The missing or open capacitor terminal fault detector is slightlydifferent from that used for the high-side switches as illustratedpreviously in FIG. 18. The second set of replicated currentscorresponding to each state (ISEN_(LB2), ISEN_(LB4), ISEN_(LB6) . . .ISEN_(LBN) in the first state; ISEN_(LB1), ISEN_(LB3), ISEN_(LB5) . . .ISEN_(LBN-1) in the second state) are each connected to currentcomparators ICP_(L1) to ICP_(LN) to detect a missing or open terminalfault at any capacitor, by detecting when the current magnitudes are ator close to zero. This zero-current detector can actually be used forthe high-side switch implementation (FIG. 18) as well but it isunnecessary to use the zero-current detector for all the high-side andlow-side switches since the FIG. 17 capacitors C₂ to C_(N) are alwaysconnected in series with a low-side switch in both the first and secondstates; only the outer capacitor C₁ is not connected in series with alow-side switch during the first state. Therefore, a zero-currentdetector for only the first high-side switch is required as shown by thecurrent comparator ICP3 in FIG. 18. Conversely, the FIG. 17 capacitorsC₁ to C_(N-1) are always connected in series with a high-side switch inboth the first and second states; only the outer capacitor C_(N) is notconnected in series with a high-side switch during the first state. Asan example, FIGS. 18-19 shows the zero-current detector used for all thelow-side switches and just the first high-side switch connected tocapacitor C₁, with both implementations together able to detect amissing or open terminal fault at any capacitor in the FIG. 17 chargepump, and not just at the outer capacitors.

FIG. 20 shows an alternate method to detect a missing or open capacitorterminal fault at any capacitor for the charge pump in FIG. 1A, althoughthis method can also be applied in the same fashion to the charge pumpsin FIG. 1B, FIG. 16 and FIG. 17. One advantage of this method is thatthe charge pump does not have to be operated with soft charging for thefault detector to work. Upon the occurrence of a missing or opencapacitor terminal fault event, either in the middle of charge pumpoperation or before charge pump operation begins, the charge pump willnot be able to regulate the output VOUT to the target set by the chargepump conversion ratio and VOUT droops lower over consecutive switchingcycles. By comparing the VOUT voltage level against a voltage thresholdVUVLO using a voltage comparator CP8, the output of voltage comparatorCP8 can be used as a logical fault indicator that disables charge pumpoperation when VOUT droops below the voltage threshold VUVLO. Thevoltage threshold VUVLO should be set below the minimum operating VOUTlevel in the application, including the largest VOUT ripple amplitudethat would occur across the application space but above a level wherebasic transistor functionality would fail or degrade to a point thatwould adversely affect the performance of the charge pump and/or asubsystem connected in series with VOUT. The voltage threshold VUVLO canbe a fixed voltage level or variable as a function of the VOUT voltagelevel and the VOUT ripple amplitude, if such information was availableto the charge pump through sensed inputs or internally programmedsettings. For instance, the charge pump switching frequency andcapacitor values could be internally programmed settings and thesesettings directly govern the VOUT ripple amplitude.

6 Implementations

Implementations of the approaches described above may be integrated intomonolithic devices, using integrated and/or external (e.g., discrete)capacitors. Control logic for detecting and processing of the detectedstates may be integrated fully on the device, or may be implemented atleast in part using external circuitry. This integrated and/or externalcircuitry can use dedicated logic circuitry (e.g., application specificintegrated circuits, ASICs) and/or software implemented logic includinga controller, processor, or some other software controlled element. Suchsoftware may be stored on a tangible machine-readable medium (e.g.,semiconductor memory, optical disk, etc.). Instructions for controllingat least some stage of design or fabrication of a device implementing anapproach described above may also be stored on a tangiblemachine-readable medium.

It is to be understood that the foregoing description is intended toillustrate and not to limit the scope of the invention, which includesthe scope of the appended claims. Other embodiments are within the scopeof the following claims.

What is claimed is:
 1. A switched capacitor power converter comprising:a first terminal for coupling to a first external circuit atsubstantially a high voltage; a second terminal for coupling to a secondexternal circuit at substantially a low voltage lower than the highvoltage, wherein in operation of the power converter charge passes on acharge transfer path between the first terminal and the second terminal;a plurality of semiconductor switch elements, including a first set ofswitch elements on the charge transfer path between the first terminaland the second terminal, wherein no switch element in the first set ofswitch elements is connected in series with either the first terminal orthe second terminal to carry substantially all the current passingthrough said terminal, and wherein each switch element in the first setof switch elements is configured to form a controllable charge transferpath between a corresponding subset of a plurality of capacitors, and asecond set of switch elements configured to form electrical connectionof at least some of the capacitors to alternating reference voltages,wherein said plurality of switch elements are configured to form saidinterconnections in successive states in operation; measurementcircuitry configured to measure a voltage and/or a currentcharacteristic of one or more switch elements of the first set of switchelements or the second set of switch elements; and fault controlcircuitry coupled to the measurement circuitry configured to alteroperation of the power converter upon detection of a conditiondetermined when the measured characteristics of the switch elementsdeviate from a predetermined range of said characteristics.
 2. Theswitched capacitor power converter of claim 1 wherein the plurality ofswitch elements further includes: a third set of switch elements on thecharge transfer path between the first terminal and the second terminalconnected in series with either the first terminal or the secondterminal.
 3. The switched capacitor power converter of claim 1 whereinthe second set of switch elements include switch elements that formelectrical connection of at least some of the capacitors to the lowvoltage terminal during some states of operation.
 4. The switchedcapacitor power converter of claim 1 wherein the stages of operationcomprise a repeated sequence of clocked stages.
 5. The switchedcapacitor power converter of claim 1 further comprising the plurality ofcapacitors, each capacitor having a terminal coupled to a terminal of atleast one switch element of the plurality of switch elements.
 6. Theswitched capacitor converter of claim 5 wherein the capacitors andswitch elements are integrated in a monolithic device.
 7. The switchedcapacitor power converter of claim 1 where the converter comprises aDickson charge pump.
 8. The switched capacitor power converter of claim1 wherein the voltage and/or current characteristics of the one or moreswitch elements belong to a group consisting of: a voltage acrossterminals of a switch element of the first set of switch elements; acurrent through a switch element of the first set of switch elements; avoltage at a junction between a switch element of the first set ofswitch elements and a capacitor of the plurality of capacitors; avoltage across terminals of a capacitor of the plurality of capacitorscoupled to the switch element; a voltage at a junction between a switchelement of the second set of switch elements and a capacitor of theplurality of capacitors; and a current through a switch element of thefirst set of switch elements.
 9. The switched capacitor power converterof claim 1 wherein the voltage and/or current characteristic of theswitch element comprises a voltage across terminals of the switchelement.
 10. The switched capacitor power converter of claim 1 whereinthe voltage and/or current characteristic of the switch elementcomprises a current through the switch element.
 11. The switchedcapacitor power converter of claim 1 wherein the voltage and/or currentcharacteristic of the switch element comprises a voltage at a terminalof the switch element.
 12. The switched capacitor power converter ofclaim 1 wherein the voltage and/or current characteristic of the switchelement comprises a voltage across terminals of a capacitor of theplurality of capacitors coupled to the switch element.
 13. The switchedcapacitor power converter of claim 1 wherein the switch elements of thesecond set of switch elements form a phase generator, and wherein thevoltage and/or current characteristic of the switch element comprises avoltage and/or current supplied by the phase generator.
 14. The switchedcapacitor power converter of claim 1 wherein each of the semiconductorswitch elements comprises a FET transistor for coupling at least two ofthe capacitors.
 15. The switched capacitor power converter of claim 14wherein at least some of the semiconductor switch elements comprise anetwork of multiple FET transistors.
 16. The switched capacitor powerconverter of claim 1 wherein at least some of the switch elements of thefirst set of switch elements or the second set of switch elements have amaximum voltage rating less than the high voltage.
 17. The switchcapacitor power converter of claim 16 wherein at least some of theswitch elements of the first set of switch elements or the second set ofswitch elements have a maximum voltage rating less than the differencebetween the high voltage and the low voltage.
 18. The switch capacitorpower converter of claim 17 wherein at least some of the switch elementsof the first set of switch elements or the second set of switch elementshave a maximum voltage rating no greater than a fraction 1/N, N>1, ofthe difference between the high voltage and the low voltage.
 19. Theswitched capacitor power converter of claim 1 wherein the fault controlcircuitry comprises one or more switches each having maximum voltagerating greater than the voltage rating of at least some of the pluralityof switches, the one or more switches being configured to electricallydisconnecting or limit current flow through at least some switchelements of the plurality of switch elements.
 20. The switched capacitorpower converter of claim 19 wherein the one or more switches comprise aswitch coupled directly to the first terminal.
 21. The switchedcapacitor power converter of claim 19 wherein the one or more switchescomprise a switch coupled between two switch elements of the pluralityof switch elements.
 22. The switched capacitor power converter of claim1 wherein the fault control circuitry is configured to modify thecharacteristics of the phases upon detection of the condition.
 23. Theswitched capacitor power converter of claim 22 wherein thecharacteristics of the phases belong to a group consisting of: a dutycycle of clocked phases; a clocking frequency of the phases; and askipping of one or more clock cycles of clocked phases.